event.pageY
gets you the mouse position relative to the entire document height(document.documentElement.offsetHeight
I assume).
But how do I get the mouse position relative to the current viewport, which is document.documentElement.clientHeight
?
For example, if the browser window size has a 720 pixel height, I scroll down 3 pages and keep the mouse in the middle of the window, the position should be "360", not 1800 (720 x 3 - 720 / 2).
Try using event.clientY
that should always return the correct value regardless of scrolling